I've used Spear and Jackson Spray and Leave and I got 2 bottles and a sprayer from Amazon for less than the price of Wet and Forget. Just make sure you buy spray and leave and not the patio cleaner (as it's not as good). I used it on my caravan, patio, fence, garden furniture etc and can't complain. I also used it on my mum's conservatory and it got rid of all the green stuff around the window joints. I'm sure wet and forget is good but it's a lot of cash and the active ingredients are probably the same in all products.
CC